<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>【案例】显示隐藏文本框内容</title>
    <script>
        function factorial(n) {  // 定义回调函数
            if (n == 1) {
                return 1;        // 递归出口
            }
            return n * factorial(n - 1);
        }
        alert(factorial(4));
    </script>
</head>
<body>
   <!-- <input type="text" value="手机" style="color: #999">
    <script>
        var text = document.querySelector('input');
        text.onfocus = function (){
            if(this.value === '手机'){
                this.value = '';
            }
            this.style.color = '#333';
        };
        text.onblur = function (){
            if(this.value === ''){
                this.value = '手机';
            }
            this.style.color = '#999';
        }
    </script>-->




</body>
</html>